In the construction of fabrics for industrial use, there are used so-called unidirectional fabrics, which confer a maximum modulus of elasticity in a particular direction, the unidirectional fabric being sandwiched between layers, e.g. synthetic-resin foils. These unidirectional fabrics are generally woven from fiberglass filaments, although, the easy fusibility of glass prevents use of such materials in high temperature applications, i.e. refractory applications such as in steel mills, foundries and the like.
Many new type fibers and materials have been proposed and laminated elements containing same have shown improvement of the order of 5 - 10 times in various physical properties, as compared to the usual fiberglass re-inforced structure using a synthetic resin.
Attempts have been made to utilize the very superior moduli, tensile strength and refractoriness of boron and boron-compounds (collectively described as boron threads or filaments) which melt at very high temperatures, and therefore display superior refractory character in the extreme high temperature environments found near hearths, furnaces, cupolas, steel converters, rolling mills, kilns and ore-roating operations. Especially disadvantageous tensile strength is found in boron whiskers.
Attempts to overcome the fragility and difficult pliability and workability of boron threads have been generally unsuccessful.
It has been proposed to solve the problem of the poor handling characteristics and workability of boron threads to provide them in the form of tapes, bands or strips with an average density of 80 threads per transverse centimeter and a width of 7 mm or greater, impregnated with epoxy or other settable resins, and to form laminated structures from a number of such bands or such bands in combination with other web-forming material. However, even the handling of these tapes, bands or webs must be delicate, and care must be taken to maintain the parallelity of the boron threads and to ensure perfect juxtaposition.
Some advantage can be gained by providing woven tapes using the boron threads as the warp (60 threads per transverse centimeter) and a synthetic resin thread as the weft (2 per longitudinal centimeter), the fabric being formed as a tape having a width of say 3 centimeters and the boron threads extending in the longitudinal direction. This woven tape to a large measure retans the disadvantages enumerated above and particularly the need to carefully juxtapose the layers. In practice the fabric tape cannot be satisfactorily used in aeronautical construction, the primary application of such fabric.